“Human exposure to benzene has been associated with a range of acute and long-term adverse health effects and diseases, including cancer and aplastic anaemia. Public health actions are needed to reduce the exposure of both workers and the general population to benzene,” states The World Health Organization.
Protecting both people and the environment while meeting the operational needs of business is an important role and a key requirement of the Code of Federal Regulations (CFR) in the U.S. Similar legislation exists worldwide with the focus on hazard identification, risk assessment and the provision of appropriate control measures, as well as health surveillance in some cases.
While toxic gases such as hydrogen sulphide and carbon monoxide are a major concern because they pose an immediate danger to life, long-term exposure to relatively low level concentrations of other gasses or vapours such as volatile organic compounds (VOCs) are of equal importance because of the chronic illness that can result from on-going exposure.
Some VOCs are hydrocarbons but not all hydrocarbons are VOCs. The latter have a significant vapour pressure at normal ambient temperature which means they evaporate or volatilize at low temperatures so they easily enter the body through normal breathing.
The benzene ring
Benzene, also known as benzol, is a common VOC, identified by its unique numerical CAS2 number 71-42-2. It is also a hydrocarbon and belongs to the benzene, toluene, ethylbenzene & xylene (BTEX) family of aromatics.
Benzene is a highly flammable colorless to light yellow liquid which occurs naturally in crude oil, natural gas and some ground waters. It is found in ambient air as a result of burning fuels, such as coal, petrol and wood, plus is common in unleaded fuel, where it is added as a substitute for lead. It is also found in cigarette smoke.
Workers can be exposed to benzene in a wide range of industries, including oil refineries, chemical and petrochemical plants, coke works, foundries and the storage, distribution and use of petrol or benzene itself.
Benzene exposure
Benzene evaporates easily and most people can just detect its distinctive smell at concentrations between 2.4 and 5 parts per million (ppm) in air.
As well as inhalation, benzene can be absorbed into the body through the skin or by swallowing material containing it. The effect on worker’s health depends on how much benzene they are exposed to and for how long. As with other organic solvents, the immediate effects of a single exposure to a high concentration (hundreds of ppm) include headache, tiredness, nausea, dizziness and even unconsciousness if the exposure is very high.
In May 2014, the U.S. Environmental Protection Agency (EPA) estimated that some five million Americans, not counting those with workplace exposures, face heightened cancer risks from benzene and 68 other carcinogens released into the air by the nation’s 149 oil refineries. This is greater than a one in one million lifetime cancer risk.
In June 2014, California officials lowered the long-term exposure level to benzene and the state is also considering classifying benzene not just a human carcinogen, but as a “toxic air contaminant which may disproportionately impact children”.
Making it clear that cancer and the other health risks posed by petroleum refineries on nearby communities are unacceptable, monitoring and control of benzene concentration levels around the perimeter of all U.S. oil refineries has been proposed by the U.S. EPA under the ‘Residual Risk Program’.
The proposed rule would revise emission control requirements for flares, storage tanks and coking units at petroleum refineries and require monitoring around refineries to ensure that neighbouring communities are not being exposed to hazardous air pollution. This proposal would also set maximum achievable control technology standards for delayed coking units, which the EPA described as a “significant” unregulated source of hazardous pollutant emissions at refineries.
The EPA said it anticipates the proposal will have a “minimal” economic effect on the refining industry but could reduce emissions of hazardous air pollutants such as benzene and xylene by an estimated 5,600 tons per year.
From a long-term (chronic) health perspective, the World Health Organization (WHO) and International Agency for Research on Cancer (IARC) classify benzene as a group one carcinogen. Prolonged exposure to high concentrations of benzene causes leukaemia and impacts red and white blood cells. The WHO has not set a standard for ambient benzene concentrations, stating that there is no safe level of exposure but many countries uses an annual average standard of 3.6g m-3 which is equivalent to 1 part per billion (ppb) or 0.001ppm.
Benzene detection
It is advisable to use an appropriate form of quantitative monitoring with the onus on the employer to do the monitoring. There are methods published by NIOSH in the U.S. that can be used to capture air samples for later analysis but by definition this occurs after exposure might have taken place. As a result, real-time methods are preferable which can range from fixed, permanent systems for fence line applications, handheld devices for area measurements or confined space entry and personal monitors that can alert a worker of an immediate risk.
What is a photoionization detector?
Known as photoionization detectors (PIDs), these instruments incorporate a UV lamp which generates high energy photons that pass through the lamp window and a mesh electrode into the sensor chamber. Sample gas is pumped over the sensor and about one percent of it diffuses through a porous membrane filter into the other side of the sensor chamber. When a photon with enough energy strikes a molecule M, an electron (e-) is ejected. The M+ ion travels to the cathode and the electron travels to the anode, resulting in a current proportional to the gas concentration. The electrical current is amplified and displayed as a ppm or ppb concentration.
A lamp can only detect those compounds with ionization energies (IE) equal to or below that of the lamp photons. So, a 10.6 eV lamp can measure hydrogen sulphide with an IE of 10.5 eV and all compounds with lower ionization energy, but is unable to detect methanol or compounds with higher IE. The choice of lamp depends on the application.
Benzene has a low IE value and is often present in a cocktail of other chemicals including aromatics. Using a proprietary 10.0 eV lamp means that only the aromatics are detected. Where the total aromatic compounds (TAC) are above the regulatory limit, a benzene pre-filter tube can be used to provide an accurate reading.
With a seemingly inexorable rise in the production and release of benzene into the environment it is vitally important that the health dangers and legislative provision are fully understood. This knowledge will help ensure employers go beyond compliance in the safety, health and wellbeing of their workforce.
To learn more, contact ION Science at marketing@ionscience.com or 1-877-864-7710.
